In a freezing apparatus or an air conditioning apparatus, what is used is a compressor that suctions a gas refrigerant evaporated by an evaporator and compresses the refrigerant to a pressure required for the gas refrigerant to condense, and feeds the gas refrigerant of high temperature and high pressure into a refrigerant circuit. As such a compressor, a rotary compressor is known. Among others, a rotary compressor having two cylinders, in which two compression chambers are structured in the compressor, is actively developed as a high-performance compressor for its characteristics including low vibrations, low noises, and capability of high-speed operations. There is a demand for a compressor of higher capacity while being small in size.
Measures taken to increase the capacity of a rotary compressor include increasing the height of a cylinder thereby increasing the capacity, and increasing the amount of eccentricity of a crankshaft thereby increasing the containment capacity of a compression chamber.
In the case where the capacity is increased by increasing the height of the cylinder, the diameter of the crankshaft must be increased in order to address increased bearing loads. Thus, the efficiency of the compressor is disadvantageously reduced.
On the other hand, the case where any measures for increasing the amount of eccentricity of a crankshaft is employed for a rotary compressor having two cylinders is discussed. In general, the crankshaft of the rotary compressor having two cylinders is provided with eccentric portions at positions opposite from each other by 180°. Pistons are respectively inserted over the eccentric portions. The crankshaft itself is supported by a main bearing that mainly pivotally supports the crankshaft, and an auxiliary bearing that pivotally supports the crankshaft on the opposite side relative to the eccentric portions, and is smaller in diameter than the main bearing. When the amount of eccentricity of the crankshaft is increased, the counter-eccentric direction of the eccentric portion of the crankshaft is positioned inward than the diameter of the main shaft, making it impossible for the piston to be inserted. A scheme for avoiding such a problem uses the difference in diameter between a main shaft portion and an auxiliary shaft portion of the crankshaft. In the scheme, a first piston to be inserted over a first eccentric portion on the side nearer to the main shaft portion is caused to pass through the auxiliary shaft portion, a second eccentric portion on the side nearer to the auxiliary shaft portion, and a connecting portion, to be inserted over the first eccentric portion. Here, the connecting portion connects between the first eccentric portion and the second eccentric portion.
In such a case, a highly efficient compressor can be realized without excessively increasing the diameter of the eccentric shaft. Further, the main shaft portion whose diameter is greater can support the load on the two eccentric portions by a greater amount. However, also in such a case, an increase in the amount of eccentricity reduces the diameter of the connecting portion connecting between the two eccentric portions, whereby rigidity of the crankshaft reduces at the connecting portion. This increases the load on the auxiliary bearing whose diameter is smaller, causing a reduction in reliability.
In view of such problems, there is a need for measures against a reduction in rigidity of the connecting portion, while avoiding a reduction in efficiency of the compressor such as an increase in diameter of the main shaft portion, the auxiliary shaft portion, and the eccentric portion.
Addressing the problems, for example in a rotary compressor described in PTL 1, a raised portion is provided at a connecting portion in a dimensional range capable of being accommodated in a bevel at the inner surface of a piston, to increase rigidity of the connecting portion.
With the conventional structure, in order to largely increase rigidity of the connecting portion, measures such as increasing the beveling diameter at the inner surface of the piston must be taken. However, since an increase in the bevel of the piston in the radial direction influences airtightness of the compression chamber, the increase in the bevel is restricted. Accordingly, there is limit in increasing rigidity.